The present invention relates to a honeycomb structure having a plurality of honeycomb segments unitarily joined by means of a bonding material layer. More specifically, the present invention relates to a honeycomb structure useful as a trapping filter for exhaust gas, particularly as a diesel particulate filter (DPF) for trapping particulate matter or the like contained in exhaust gas from a diesel engine, and capable of effectively inhibiting generation of defects such as cracks due to thermal stress by lightening an influence of thermal stress generated upon production.
A honeycomb structure is incorporated in an exhaust system or the like of a diesel engine as a trapping filter for exhaust gas, for example, as a diesel particulate filter (DPF) in order to trap and remove particulate matter contained in exhaust gas from a diesel engine or the like. Such a honeycomb structure has a problem of generating defects such as a crack due to thermal stress generated on an outer peripheral coat layer (particularly, in a portion located on an end face in the longitudinal direction of the bonding material layer in a cross-section in a direction perpendicular to a central axis direction). Though it can be considered to lower a cooling rate in order to reduce such defects, it is not the best measure since it lowers productivity.
Particularly, a honeycomb structure of silicon carbide is expected because it is excellent in thermal resistance. However, it has a high thermal expansion coefficient (high thermal stress generated) and low thermal shock resistance in comparison with a cordierite honeycomb structure, and the aforementioned problem is amplified. Further, remarkable increase in thermal stress caused in accordance with recent increase in size of a filter causes more serious generation of defects such as a crack more frequently to higher extent.